class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        if not nums:
            return None
        d ={}
        for i,item in enumerate(nums):
            tmp = target - item
            for key,value in d.items():
                if value == tmp:
                    return [i,key]
                
            d[i] = item 
        return None
